Die casting and similar molds with accelerated venting means

ABSTRACT

A MOLD FOR RECEIVING PRESSURE INJECTED MOLTEN MATERIAL CHARACTERIZED IN PART BY THE INCORPORATION OF AIR VENTING MEANS ASSOCIATED WITH THE RUNNER SYSTEM OF THE MOLD AND INCLUDING VENTING MEANS DISPOSED CLOSELY ADJACENT EACH GATE BETWEEN A RUNNER AND A CAVITY SERVED BY THE RUNNER.

- Feb. 9, 1 1971 DIE CAYSTIINQAND SIMILAR MOLDS WITH ACCELERATED VEN'IING MEANS Fi led odt. 17.11967 I 2 Sheets-Sheet 1 INVENTOR. HARRY R. BUCY ATTORNEYS J & v Q

Feb. 9, 1971 Y H. R. BUCY 3,561,061 I DIE CASTING AND SIMILAR MOLDS WITH ACCELERATED VENTING MEANS Filed Oct'. 17.- 1967 2 Sheets-Sheet 2 5756 blag- 43 49 i x N INVENTOR. HARRY R. Bucy BY 410.42. 1

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A T TORNE KS United States Patent Oflice 3,561,061 DIE CASTING AND SIMILAR MOLDS WITH ACCELERATED VENTING MEANS Harry R. Bucy, 625 S. Glenwood Place, Burbank, Calif. 91506 Filed Oct. 17, 1967, Ser. No. 675,852 Int. Cl. B29f l US. CI. 18-30 21 Claims ABSTRACT OF THE DISCLOSURE A mold for receiving pressure injected molten material characterized in part by the incorporation of air venting means associated with the runner system of the mold and including venting means disposed closely adjacent each gate between a runner and a cavity served by the runner.

BACKGROUND OF THE INVENTION (1) Field of the invention The field of the invention is that relating to molds for receiving pressure injected molten material in classes 18 and 22.

(II) Prior art The prior art known to applicant includes his prior patents 3,108,339 dated Oct. 29, 1963, 3,266,098 and 3,266,099 both dated Aug. 16, 1966 and 3,357,057 dated Dec. 12, 1967, together with the patents cited as references in said patents and said application.

SUMMARY OF THE INVENTION The invention is generally concerned with separable molds into which molten material is injected under pressure and is directed to means for facilitating the escape or expulsion of the air and gas in the injecting means, e.g. a shot cylinder, in the mold sprue hole and runner system, and in the mold cavity or cavities in advance of the entering molten material and in which the entering molten material is not obliged to compress the air or gas thus being expelled to a magnitude in excess of atmospheric pressure. In other words, the venting means associated directly with the mold cavity need not be such as will accommodate the expulsion of all the air and gas which is displaced from the molten material injecting means, e.g., a shot cylinder, the sprue hole, and the runner system as well as the mold cavity or cavities. This, among other advantages, reduces the likelihood of porous castings from entrapped air and gas. Accordingly, the specific objectives of this invention may be stated as follows:

An object of the invention is to provide a venting means for accelerating the removal of air from the shot cylinder, sprue hole and runner systems of a mold upstream of the casting cavity or cavities of the mold.

Another object of this invention is to provide a means of venting the beforementioned air ahead of the mold cavity or cavities in a manner that will not require it to be compressed above atmospheric pressure for it to begin to move out of the mold through the venting means to the atmosphere.

Still another object of the invention is to prevent the air in a mold cavity or cavities from being compressed above atmospheric pressure at the time the metal enters the cavity. 7

A further object of the invention is to prevent the air in the mold cavity or cavities from having to be compressed above the atmospheric pressure before it can start to flow therefrom to the atmosphere.

A still further object of the invention is to increase 3,561,061 Patented Feb. 9, 1971 the length of time that the air is actually moving out of the mold cavity or cavities to atmosphere in the casting cycle.

Still another object of the invention is to permit vacuum to be employed in the mold to aid in the making of a casting without the need of special equipment on the machine to prevent the material from being sucked into the mold prior to the injection cycle of the machine.

A still further object of the invention is to prevent creation of a Windstorm by the application of vacuum to the cavity with resultant carrying of droplets of molten material to the source of air movement to and from the cavity and closing it off prior to the filling of the cavity.

Still another object of the invention is to provide a method of combining a vacuum application with open to atmosphere venting not involving the mold parting line for the improvement of the casting.

Another object of this invention is to prevent any of the air or gases anywhere in the mold from ever being compressed above atmospheric pressure.

DESCRIPTION OF THE DRAWINGS In the accompanying drawings, which form a part of the specification describing a presently preferred embodiment of the invention;

FIG. 1 is an elevational view of the cover die end surface of a mold embodying the invention,

FIG. 2 is a side elevational view of the mold viewed 0 from the left hand side of FIG. 1,

FIG. 3 is an enlarged plan view of the cover die component at the parting line of the mold as on the plane of the line 3-3 of FIG. 2,

FIG. 4 is a sectional view of the mold taken in the plane of the line 44 of FIG. 3,

FIG. 5 is a further enlarged view of the portion of FIG. 4 contained in the circled area thereof,

FIG. 6 is a plan view of the ejector die component at the parting line of the mold as on the line 66 of FIG. 2, on the same scale as FIG. 3,

FIG. 7 is a sectional view of the mold taken in the plane of a line 7-7 of FIG. 6,

FIG. 8 is a plan view of the outer face of the cover die shoe component indicated by the line 88 of FIG. 2,

FIG. 9 is a plan view of the cover die shoe cover plate indicated by the line 99 of FIG. 2, the view showing the cover plate as though swung up from FIG. 8,

FIG. 10 is a fragmentary section taken on the line 1010 of FIG. 3, and,

FIGS. 11 and 12 are perspective views of the parts being cast in the illustrated mold DESCRIPTION OF PRESENTLY PREFERRED EMBODIMENT Since the principles of the invention are applicable to all forms of pressure injection molds and since equivalent parts of molds for different types of molding machine molds are known by diiferent names, it will be understood that the terms hereinafter used will be for convenience in terminology and will be assumed to include all equivalent parts regardless of the name by which those equivalent may be known. For example, the term sprue hole will be understood to include any opening through which molten material is introduced by pressure into a mold for delivery into a mold cavity by a runner. Likewise, breather will designate a device including converging conical surfaces which combine to form an annular orifice of gradually decreasing radial dimension through which only air and gas may flow but through which the molten material, by reason of viscosity thereof, cannot flow, such breathers being specifically described in my prior Pat. No. 3,108,339 above cited.

Referring to the drawings, the illustrated embodiment comprises a mold including cover and ejector die components 1 and 2. The cover die component includes a die shoe 3 having a cavity in which a mold cavity insert 4 and a sprue hole insert 5 are disposed. The outer end face of the cover component carries a cover plate 6 secured thereto by screws 7 for purposes later to be explained.

The ejector die component includes a die shoe 8 having a cavity in which die inserts 9 and '10 complementary respectively, to the inserts 4 and 5 are contained. Alignment between the die components (hereinafter referred to as half or halves is maintained by lead pins 11 carried by the ejector half and on which complementary bushings 12 carried by the cover half are slidable as the mold is opened and closed. Where necessary, ejector pins 13 are provided, a few being shown in FIGS. 6 and 7. Other usual components of molds of the above character such as the screws by which the die inserts are secured in their respective die shoes, the ejector plate and operating means therefore are omitted as being unnecessary to an understanding of the invention.

Before going into the specific details of the present invention, and prior to applicants said prior patents, the general state of the art was as stated, for example in the book entitled Die Casting by H. H. Doehler, published by McGraw-Hill Books, copyright 1951 at page 84 under the heading Venting, and in the same book a portion of Chapter thereof beginning on page 426 and extending through and including page 438.

Applicants said prior patents, as does the present invention, contemplate the making of pressure injected molded parts usually without any flash whatever to be trimmed away from the resulting casting. In the said prior patents, this was achieved by the use of vents called breathers which communicated with the atmosphere from a point of the mold cavity surface other than at the mold parting line and which were so designated for the reason that they atforded means for the flow of air and gas into and out of the mold cavity and runner. A problem not solved by the inventions of the said prior patents was achieving the expulsion of the air and gas in the molding machine shot cylinder or its equivalent, in the sprue hole, runner system and cavity or cavities of the mold without being compressed and, consequently without imposing back pressure on the entering molten material. Other than said applicants said prior patents and application, it has been assumed that this air and gas must be expelled through narrow parting line vents such as described in the cited books and this, of necessity, involves subjecting that air and gas to a high degree of compression. One solution of this problem is that in applicants said pending application in which the mold cavity and all spaces to be occupied by the molten material are maintained in an evacuated condition. This is a very satisfactory solution of the problem so far as quality of castings are concerned and serves in those instances in which the casting quality is the primary consideration. The mold is, however, costly to make and except for those instances in which there must be the most absolute maintanence of maximum quality of casting, is not necessary, particularly in the light of the present invention which achieves commercially acceptable results with a less costly die.

In the illustrated embodiment of the invention, the die inserts 4 and 9 are provided with complementary portions forming cavities in which the castings 14 and 15 (see FIGS. 11 and 12) are formed, the portions of said cavities in the cover half being designated as 140 and 15c and the portions thereof in the ejector half being similarly designated as Me and 150. The casting 14 includes a hole 16 extendingtherethrough, said hole being formed by the core element 17 seated in the ejector die insert 9, and said core element, beyond the face of said casting in the cover die insert being utilized to form one component of a breather" by being slightly tapered as at 18 disposed concentrically within the slightly greater tapered portion 19 of a concentric bore 20 in the cover die insert 4 and terminating in a cylindrical end portion 18 disposed in the bore 20 and combining therewith to form an annular passage through the narrowest portion of which air and gas can escape but through which the molten material, by reason of the viscosity thereof cannot flow. Beyond the tapered portion 19, the bore 20 continues as a straight bore through the insert 4 and the die shoe 3 and is met by the inner end of a groove 21 in the adjacent face of the plate 6 which combines with the back surface of the die shoe 3 to form a passage communicating with atmosphere at the top of the mold, (assuming that the mold is being used in the machine in which the ejector half is moved horizontally towards and away from the cover half).

Since the casting 15 has no opening extending therethrough, a secondary cavity 22 is formed adjacent to the portion of the casting cavity which is most remote from the runner by which molten material is delivered to the casting cavity, said secondary cavity being relatively shallow and being connected to the cavity 15c by a gate 23. A breather assembly, generally like that already described and including a core member 24 extending through the cavity 22 from the die insert 9 and having a tapered end surface cooperating with a correspondingl tapered end of a bore 25 extending through the die insert 4 and die shoe 3 serves to allow air and gas to escape while serving to prevent the escape of molten material in the same manner as has been previously described. The inner face of the cover plate 6 is provided with a groove 26 generally similar to the groove 21 and similarly extending to the top surface of the mold and combines with the end face of the cover die shoe to form a passage for expelled air and gas to be conducted to atmosphere.

The cover half is provided with a sprue hole 27 for the introduction of a molten material, said sprue hole extending through the die shoe 3 and die insert 5 from a counterbore 28 in which the delivery end of the shot cylinder is received, said counterbore extending through the cover plate 6 and partially through the end portion of the die shoe. The die inserts 4, 5, 9 and 10 are provided with opposed grooves which combine to form a runner system between the sprue hole and the cavities for the castings 14 and 15, said runner system comprising a main runner 29, a first branch runner 30 extending between the main runner 29 and the cavity for the casting 14 and a second branch runner 31 extending between the main runner and the cavity for the casting 15, said branch runners terminating at the juncture with respective cavities with shallow gate portions designated respectively as 30a and 31a to provide weakened portions at which the castings may be readily snapped off the runner casting.

Since, as an incident to making a shot, the mold cavities, runner system, sprue hole and the shot cylinder are filled with air which must be expelled either by the advancing molten material or by other means, if the venting means associated with the casting cavity or cavities is insufficient to permit the ready expulsion of the air by the entering molten material, a back pressure will be created which in its least objectable result will effect a slowing up of the rate at which the cavities are filled and at its worst condition will result in porous or only partially filled cast ings. In pressure die casting, the time factor in which a shot is made is exceedingly short, being usually of the order of about A to about /2 second in duration and seldom even on the largest castings, taking as long as one second.

The present invention proposes to facilitate the entrance of the molten material by allowing and even facilitating the removal of at least a major portion of the air and gas from the shot cylinder, sprue hole and runner system in advance of the entering molten material so that, in effect, the only air which is actually required to be expelled by the entrance of the molten material into the mold cavities is little if any more than that which is contained within the mold cavities at not more than atmospheric pressure. This then permits the molten material to move into the cavity virtually unopposed by any pressure and with resultant significant reduction of the cavity filling time.

This removal of air and gas is achieved primarily by the use of breathers connected to the runner system at appropriate points to be described, said breathers being connected exteriorly of the mold to evacuating means here shown by way of example as jet pump devices, which may, for example, be of the type shown in Pat. 3,108,339 and which, upon activation, will operate to exhaust the air and gas from the runner system. Any other equivalent evacuating means could, of course, be employed. In the mold illustrated, the main runner 29 extends beyond the most remote of the branch runners, in this case, the branch runner 30, and terminates in an enlarged cavity 32 formed in the ejector half and through which cavity a breather core member 33 extends, said core member terminating in a tapered distal portion 34 and a cylindrical end portion 34' which cooperate with the complementarily tapered end 35 of a bore 36 extending through the die insert 4 and die shoe 3 and with the bore 36, the end 34' and bore 36 (see FIG. serving to form an annular passage of gradually decreasing width and through the downstream end of which, prior to being sealed by incoming molten material, air and gas may pass but which is of such a narrow width that the molten material will not pass. Similar breathers 37 and 38 are connected, respectively to the branch runners 30 and 31 adjacent the connection thereof with the cavities served by those branch runners, the core components of said breathers extending through cavities 37a and 38a, the cooperating bores extending through the cover half are designated as 37b and 38b. As here shown these breathers are slightly smaller in diameter than the main runner breather and this will generally be true. The diameter of any one such breather is such as will exhaust the portion of the runner served thereby within the limited time interval for such action.

The underside of the cover plate 6 is provided with a Y-shaped groove 39, the forked ends of which terminate in registry with the bores 37b and 38b and the juncture of said forked ends is disposed in registry with the bore 36. The stem portion thence continues toward the nearest side of the mold and terminates midway between that side and the cavity in which the cover half die insert 5 is disposed. A bore 40 extends into the die shoe wall from a point in registry with the end of the stem portion of the groove 39 and intersects a bore 41 extending inwardly from the outer face of the die shoe, said bore 41 communicating with the intake orifice of a jet pump device 42 such as illustrated and described in detail in the said prior Pat. 3,108,339 of the applicant. When the jet pump 42 or an equivalent source of vacuum is activated, it will exhaust the air in the runner system and, additionally, will draw air from the cavities 14 and 15, the air thus being drawn being replaced by air entering through the breather assemblies 18-19 and 24-25 associated therewith. Thus, the elfect of the runner breathers is to insure that at no time will there be a greater than atmospheric pressure in the mold cavity or cavities and at the instant that the incoming molten material has reached a gate of a casting cavity, the only air to be expelled is that which occupies the casting cavity and the vent means for the cavity, per se. In this connection, it having been observed in the tryout of the new molds, particularly those in which there is unobstructed flow from the gate to the most remote part of the mold, that if porosity or cold shuts are observed, those defects are most likely to be found, not

at a point in the casting remote from the gate but at a point not far removed from the gate. This means that the cavity fills from its most remote point progressively towards the gate and consequently air venting means should accommodate the manner in which a mold cavity fills. In this connection, reference may be had to the book 6 Die Casting by H. H. Doehler, copyright 1951, published by McGraw-Hill Books Company, Inc., pages 126-134 which describe the manner in which a mold cavity fills.

To meet this condition, in addition to the runner evacuating means above described, in those instances in which it may otherwise be difficult to insure that the cavity will be completely filled with non-porous material, it is advisable to provide an additional evacuating means to assist in the displacement of air in the casting cavity or cavities by the incoming molten material and which is complementary to the manner in which a mold cavity is filled. A means for this purpose is illustrated in the drawings comprising pairs of grooves generally parallel to at least a portion of the outline or perimeter of each of the cavities and generally parallel to each other, preferably formed in the ejector die face. As here shown, a primary groove 43 extends in spaced relation about the sides of the cavity Me which are adjacent to the side and the surfaces of the die insert 9 and a secondary groove 44 of lesser width is interposed between the groove 43 and the cavity and extends in uniformly spaced relation to the edge of the cavity from a point spaced from the runner breather 37 to a point adjacent the opposite side of the runner 30. The primary groove 43 is provided with a pair of breathers 45, 45 at appropriate points in the length thereof, the associated bores 46, 46 thereof extending through the die insert and die shoe into communication with a groove 47 in the inner face of the cover plate 6, said groove (see FIG. 10) terminating in communication with a bore 48 in the die shoe 3 which, in turn, by an intersecting bore 49, is connected to the intake orifice of a jet pump device 50 on the exterior of the cover die shoe 3. The casting cavity 15 is similarly provided with a primary groove 51 spaced from the edge of the cavity 15e and an interposed secondary groove 52. A pair of breathers 53, 53 similarly disposed in the primary groove 51 communicate through bores 54, 54 with a groove or channel 55 in the plate 6 and are connected to the intake orifice of a jet pump 56 in the same manner as shown in FIG. 10. Referring to the drawings, it will be understod that the core and bore components of the breathers 37, 38, 45 and 53 have configurations similar to the configuration of the larger sized breathers illustrated and that due to the smaller size of these breathers, the indication of the tapered portions thereof by concentric circles has been omitted as impractical to illustrate.

Normally, the clearance between the adjacent faces of the die inserts in the areas between the primary and secondary grooves and between the secondary groove and cavity is so minute that molten material will not pass therethrough. However, in the event that it is desired to assist the breather or breathers associated with a castmg m permitting the air to be expelled with still less resistance, reducing the width of the lands comprising the opposing portions of the die face surfaces thus defined by the cavity and the spaces between the primary and secondary grooves, as by total or selective widening of the secondary groove, will facilitate the flow of air from the cavity to the primary groove under the influence of the breathers without making a clearance of such depth that the molten material can enter. Thus, the function of the secondary groove, is to make it possible to vary the width of the opposing portions or lands of the die faces between the cavity and the primary groove so that the rate of escape or expulsion of air from the cavity at points along the perimeter of the cavity can be regulated by increasing or decreasing the Width of the secondary groove. Moreover, this variation in width can be effected at different points along the secondary groove depending on the manner in which the cavity fills with the molten material when such selective widening will serve to effect the desired manner in which the mold cavity will be filled. It is to be remembered, as above explained, that the filling of a mold with molten material takes place quickly and usually in a very small fraction of a second and that despite 7 this time limitation, the resulting casting is intended to be formed without porosity and without flash of such size as would require the use of a trimming process. This last described phase of the invention affords means by which both the rate of filling the mold cavity can be increased and by which, through selective variation of the width of the secondary groove, the flow of the molten material can be manipulated so as to move quickly and completely fill the mold cavity. In extreme cases, the vent formed by the opposing die face areas between the cavity and second groove may be increased at some portion or portions along the area to allow the molten material to enter the second groove and partially or completely fill it and thus serve as a surplus material cavity to insure that the cavity will be filled without blowholes or other defects in the resulting casting.

While in the foregoing specification, a presently preferred embodiment of the invention has been described, the invention is not to be deemed to be limited to the precise mold illustrated by way of example and it will be understood that the principles of the invention can be applied to the design and manufacture of molds for articles of varying shapes without departure from the principles of the invention. For example, the runner system and number of branch runners could be greatly varied and under some conditions a single runner breather might serve the runner connected to more than a single cavity or, if the mold involved has two or more separate and substantially identical cavities disposed at substantially equal distances from the sprue hole, a common practice is to provide separate runners from the sprue hole to each of the cavities, and in such event, only the breathers at the gate of each cavity would be employed. Moreover, such considerations as die face area limitations may preclude optimum placement of the main runner air expulsion means at the downstream extremity of the main runner while permitting the location thereof closer to the point of entry of the molten material. While the said optimum location is, of course, preferred, so long as the major portion of the air and gas to be displaced by the entering molten material is expelled without being subjected to disadvantageous compression, the objective of the invention is realized. In this connection it will be remembered that the vent orifices connected with the runner and cavity and which are served by jet pump devices are much smaller in cross sectional area than that of the passage or conduit extending to the jet pump intake. As a consequence, the volumetric dimension of the conduit or passage serves, in effect, as a vacuum storage tank having a fixed intake orifice in accommodating the air and gas displaced by the advancing molten material.

Similarly, the last described groove surrounding the cavities might be otherwise arranged and the primary groove might have more or less than the two breathers here shown by way of example, dependent upon such factors as the volumetric and peripheral dimensions of the cavity and the flow pattern of the molten material in filling the cavity. In the light of these considerations, it will be understood that the invention includes all such modifications and changes in the parts and the construction, combination and arrangement of parts as shall come within the purview of the appended claims.

I claim:

1. In a mold having halves separable at a parting line and, when juxtaposed, defining at least one cavity into which molten material is injected under pressure and a runner means operative to conduct the injected molten material to the cavity, means for accelerating the expulsion of air and gas displaced by the advance of the molten material toward the cavity while maintaining the unfilled portion of the runner means at substantially atmospheric pressure, said expulsion accelerating means comprising at least one negative pressure creating device and having an intake orifice connected by a conduit means extending through one of said halves to the runner means at a point downstream of the point of connection of the runner means with the cavity, said conduit means adjacent to said connection with said runner means including a portion of such narrow Width that only air and gas can pass therethrough to the device intake orifice, but through which the molten material, by reason of the viscosity thereof cannot pass, and an air ingress means having communication with the cavity operative to prevent said device from creating a negative pressure in said runner means.

2. A mold as claimed in claim 1 in which said narrow width portion of said conduit means is disposed at the juncture of said conduit means with the runner means and is of such lesser cross sectional area than the cross sectional area of said intake orifice that said conduit means, when subjected to negative pressure by said device, acts as a vacuum storage tank having a restricted inlet orifice.

3. A mold as claimed in claim 1 which said runner means is also served by a second air and gas expulsion accelerating means corresponding to said first accelerating means and including a conduit means having a narrow width portion connected to said runner means adjacent to the jucture of said runner means and said cavity.

4. A mold as claimed in claim 1 in which said runner means includes a main runner and at least one branch runner extending between said main runner and said cavity, and in which a second air expulsion accelerating means including a second negative pressure creating device having an intake orifice is connected by a second conduit means with said branch runner at a point closely adjacent the juncture of said branch runner with said cavity; said second conduit means including means for preventing entry of molten material corresponding to that I incorporated in said first conduit means.

5. A mold a claimed in claim 1 in which said cavity is in communication with a first vent means affording the passage of air and gas only therethrough in either direction between said cavity and atmosphere, said vent means including a conduit means disposed wholly in one of the halves constituting said mold.

6. A mold a claimed in claim 1 in which the periphery of said cavity is in communication with a second vent means comprising a groove formed in the face of at least one of said mold halves and extending generally parallel to and spaced from a portion of the cavity perimeter, at least a portion of the opposing die faces in the area defined by said groove and cavity perimeter being spaced apart when the mold is closed, and at least one passage extending wholly through one of the mold halves from communication with said groove to an exterior surface of that mold half and including a vent portion adjacent to said groove through which air and gas only can pass.

7. A mold as claimed in claim 1 in which said cavity at the area defined by the cavity perimeter and said groove in the face of one of the mold halves spaced from and generally parallel to at least a portion of the perimeter of the mold cavity, the opposing faces of the mold halves at the area defined by the cavity perimeter and said groove being spaced apart, a negative pressure creating a device connected by a conduit means to said groove operative to create a negative pressure in said conduit means sufiicient to accommodate air and gas expelled from said cavity into said groove by the entering molten material, and a vent means interposed at the juncture of said conduit means with said groove.

8. A mold as claimed in claim 6 in which a second groove is interposed between said cavity perimeter and said first named groove.

9. A mold as claimed in claim 1 in which said mold includes a plurality of cavities, in which said runner means includes a main runner and a system of branch runners extending between said main runner and each of said cavities in which a plurality of separate air expulsion accelerating means are separately connected to one each of said cavities by conduit means each extending through one or the other of said mold halves from the intake orifice of the associated air expulsion accelerating means and in which each of said conduit means is in communication with a ventmeans bordering at least a portion of the perimeter ofthe associated cavity.

10. A mold as claimed in claim 9 in which each of said plurality of cavities includes a separa e vent means open to atmosphere through one of said mold halves operative to allow the ingress of air to the cavity incident to replacement of air exhausted from the cavity with which it is associated by the associated air expulsion accelerating means and to serve as an additional egress means for air and gas from the cavity incident to the displacement thereof by the entering molten material.

-11. A mold as claimed in claim 9 in which said means for accelerating the expulsion of air and gas from each mold cavity includes a pair of grooves formed in the face of at least one of said halves and extending generally parallel to and spaced from the juncture of a portion of the cavity with which it is associated and the die face, and at least one passage extending wholly through one of the mold halves from communication with the outermost of said grooves to the exterior of that mold half and including a narrow width orifice in communication with said groove through which air and gas only can pass.

12. In a mold having halves separable at a parting line and, when juxtaposed, defining a cavity into which molten material is injected under pressure and a runner means operative to conduct the molten material to the cavity, the combination of means for accelerating the expulsion of air and gas displaced by the advance of the molten material toward said mold cavity, other means operative to maintain the unfilled portion of said runner means and said cavity at substantially atmospheric pressure during such advance, and a second air expulsion accelerating means including a gI'OOVc formed in the face of one of said halves and disposed generally parallel to and spaced from at least a portion of the perimeter of said cavity, and an air conducting conduit means extending wholly through one of the mold halves and connecting said groove with the intake of an evacuating device, the juxtaposed faces of said mold halves at the area defined by said cavity and said groove being spaced apart and the juncture of said conduit means with said groove including a vent means operative to allow the passage therethrough only of air and gas.

13. A mold as claimed in claim '12 in which a second groove extending generally parallel to said first groove, and in which at least a portion of the die faces in the area defined by the adjacent edges of said second groove and the cavity perimeter are spaced apart a distance suificient to allow the molten material to flow into said second groove.

14. In a mold having halves separable at a parting line and, when juxtaposed, defining a cavity into which molten material is injected under pressure and a runner means operative to conduct the molten material to the cavity,

the combination of means for the positive evacuation of air and gas displaced from the cavity by the entrance of the molten material into the cavity while maintaining the unfilled portion of the cavity substantially at atmospheric pressure, said evacuating means including a groove formed in the face of at least one of said halves and extending spaced from and at least substantially parallel to at least a portion of the perimeter of the cavity, an air evacuating means having an intake orifice connected to said groove by a first conduit means extending through said one of said mold halves, the spacing between the opposing faces of said mold halves in the area defined by the adjacent edges of said cavity and said groove being sufficient to permit the passage of air and gas only from said cavity into said groove, and a second conduit means extending between said cavity and atmosphere disposed wholly in one of the mold halves, and including an orifice adjacent to the cavity through which air and gas only can pass, said second conduit means being operative to prevent said cavity from being evacuated below atmospheric pressure by said evacuating means.

15. A mold as claimed in claim 14 in which the width of said area between said groove and said cavity is reduced by the interposition of a second groove of less width than the Width of said area between said cavity and said first groove and extending longitudinally of said area for at least a portion of the length of said area.

16. In a mold having halves separable at a parting line and, when juxtaposed, defining at least one cavity into which molten material is injected under pressure and a runner means operative to conduct the injected molten material to the cavity, the combination of means for increasing the capacity of the mold to expel air and gas from said runner means to accommodate the advance of the molten material toward the cavity at substantially the volumetric rate of such advance, said expulsion cacity increasing means including a conduit means connected to said runner means at a point downstream of said point of connection with said runner means, said con duit means thence extending from said runner means through one of said halves and including an orifice portion closely adjacent to said point of connection to said runner means of such narrow width that only air and gas can pass therethrough, and means for imposing a negative pressure in said conduit means.

17. A mold as claimed in claim 16 in which said mold includes a plurality of cavities, in which said runner means includes a main runner extending to said air expulsion capacity accelerating means and at least one branch runner extending between said main runner and one of said cavities, in which said air expulsion capacity increasing means is connected to said main runner adjacent to and downstream of the juncture of said runners, in which at least one additional and corresponding air expulsion capacity increasing means is connected to said branch runner adjacent the juncture of said branch runner with the cavity served thereby and in which a second conduit means extends from said second expulsion acceleration means to atmosphere.

18. A mold as claimed in claim 16 in which said mold includes a plurality of cavities served by runner means extending from the point of entry of the molten material to each of said plurality of cavities, in which a plurality of separate conduit means extends between one each of said runner means and one each of a plurality of separate air expulsion capacity increasing means, and in which each of said conduit means includes a narrow width portion similar to that associated with said first named conduit means.

19. A mold as claimed in claim 18 in which each of said plurality of cavities includes a separate means operative to allow the ingress or egress of the air and gas only in said cavities incident to evacuation by said ex pulsion capacity increasing means or to displacement by the entering molten material.

20. A mold as claimed in claim 16 including means for increasing the capacity to expel air and gas from the mold cavity and comprising a pair of grooves formed in the face of at least one of said halves and extending generally parallel to each other and spaced from each other and from a portion of the perimeter of a portion of the cavity with which it is associated, at least one passage extending wholly through one of the mold halves from communication with the outermost of said pair of grooves to the exterior of that mold half and including a narrowed portion adjacent to said outermost groove through which air and gas only can pass, and a separate means for creating a negative pressure connected to said passage at a point remote from said narrowed portion.

21. In a mold comprising separable halves defining at least one cavity and a runner means for conducting injected molten material to the cavity when said halves are juxtaposed, the combination of means for facilitating the advance of injected molten material along said runner means toward said cavity, said material advance facilitating means comprising a passage extending through one of said halves from an orifice communicating with said runner means at a point remote from the upstream extremity of said runner means to an end of said passage having connection with a source of negative pressure, said orifice being of such narrow width that only air and gas may pass therethrough from said runner means, and other means operative to oppose the efiect of negative pressure in said passage on said runner means by maintaining the unfilled portion of said runner means substantially at atmospheric pressure as said runner means is filled by the entering molten material.

References Cited UNITED STATES PATENTS Knowles 1830 Ohse 16 1-305X Jagielski 164-305X Bucy Bucy -164305X Bucy 164305X Grigull 18-30 Bucy 18-30 US. Cl. X.R. 

